Touch screens are well known on many devices such as personal digital assistants, payment terminals, and portable computers. The most common touch screen uses flexible membrane technology, but these membranes are not durable and the membranes are positioned over the display, reducing the brightness and contrast of the display.
Another touch-screen technology uses infrared (IR) light-emitting diodes (LEDs) positioned around the periphery of a screen. One type consists of an array of photosensors along two sides of a display, and a corresponding array of IR light sources, such as LEDs, along the opposite sides. The photosensors detect when an object touches the screen by detecting that IR light from the opposite LED is no longer visible to a sensor. This technology works well, but for adequate resolution it requires such a dense population of sensors and LEDs that it can become too expensive and too power-hungry for some applications. In addition, such an arrangement is not scalable, meaning that custom arrays of LEDs and sensors must be created for each screen size.
Another type of technology replaces the IR photosensors with a smaller number of cameras, but these cameras are bulky, making the touch-screen large, thick, heavy and not very user-friendly.